Party line selective signalling system having code and conference call



p 1955 c. E. LOMAX 2,717,925

PARTY LINE SELECTIVE SIGNALLING SYSTEM HAVING CODE AND CONFERENCE CALL Original Filed April 12, 1950 12 Sheets-Sheet 1 FIG. I

INVEN TOR. CLAR ENGE E. LOMAX ATTY.

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MULTI GROUP CONFERENCE TO snow *I TO caou z TO OTHER GROUPS ATTY United States, Patent PARTY LINE SELECTIVE SIGNALLING SYSTEM HAVING CODE AND CONFERENCE CALL Clarence E. Lomax, Chicago, Ill., assignor to Automatic Electric Laboratories, Inc., Chicago, [1]., a corporation of Delaware Original application April 12, 1950, Serial No. 155,546. Divided and this application August 27, 1952, Serial No. 306,608

7 Claims. (Cl. 17918) The present invention relates in general to automatic telephone systems, but is more particularly concerned with small systems which are commonly known as private automatic exchanges, or as a P. A. X, and is division of my prior application filed April 12, 1950, Serial No. 155,546. Exchanges of this nature are usually installed by private concerns, and in order to meet the more exacting requirements of the subscribers in these small systems, it is often necessary to provide various special features which are unnecessary in a large public exchange. The present invention is concerned with the abovementioned special features which are commonly known as code calling, conference calling, executive cutin or right-of-way and party line service.

The principal object of the invention is to provide certain new and improved circuit arrangements, whereby, the above-named special features are provided without materially increasing the cost of the equipment, while retaining simple, efiicient and modern high-class telephone service.

One of the features of the invention relates to improved circuit arrangements, whereby, the rotary switch as described in the co-pending application of Kenneth W. Graybill et al., Serial No. 654,556, filed March 15, 1946, is utilized in applicants illustrated finder, connector, code call and conference call equipment.

Another feature of the invention relates to an improved line equipment and circuit, whereby, during conference calls other parties on the lines that contain a conference member are totally disconnected from their respective lines during the conference call.

Another feature of the invention relates to improved circuit arrangements, whereby, party line service, code call, conference service and executive cut-in service can all be given in the same exchange.

Still another feature relates to conference service, whereby, various types of conference service can be provided, with the requirements of the particular exchange controlling the type service to be used.

Other features, together with the ones named above, will be explained hereinafter, reference being had to the accompanying drawings which show by means of the usual circuit diagrams a suificient amount of apparatus to enable the invention to be described and understood.

Referring now to the drawings, Figures 1 to 15, inclusive:

Figure 1 shows four lines having two substations each,

such as A and A on one line and D and D on another, etc. Substations A, B and C are shown as conference members, hence, the cut-through relays such as 100, and are provided. Substation A is shown as belonging to an executive and is provided with the executive cutin non-locking push button 178. Substation A is also provided with the non-locking push button 168 which enables the originating of the key-type conference call (push button 168 is used only when Figure 2 is a part of the exchange). The line containing substations D and D is provided with no special features and therefore,

only local or regular calls can be handled. Combined line and cut-01f relays such as 130, 140, and are individual to each line.

Figures 2, 2A and 2B are used only when the exchange is to include conference calling, with each of the Figures 2, 2A and 2B being individual to a certain type of conference service. It is to 'be remembered that only one type conference can be used at a time, therefore, only one of the Figures 2, 2A or 2B can be used at a time. It will be noted that each of the figures have been drawn so as to be easily substituted for the other and to readily connect between Figure 1 and the adjoining figures. It will also be noted that the ring cut-off and battery feed relays individual to each line that is provided with conference service, are given the same number and location in each of the figures and that the functions of the above mentioned relays are identical in each figure. However, the relays in the respective right-half portions of each figure are different. In Figure 2 a single conference group is provided, substations A, B, and C being the conference members, with one of the substations such as A having a key for initiating the conference call. In Figure 2A two-conference group service is shown with substations Aand C being individual to groups 1 and 2 respectively and substation B being common to both groups. In Figure 2B multi-group conference service is shown, with only two groups illustrated. Substations A and C are again in dilferent groups and substation B is common to both.

Fgiures 3 and 4 show one of the finder-connector links of the exchange.

Figure 5 shows the distributor.

Figures 6, 7 and 8 show the code call equipment, with Figure 6 showing the code call finder, Figure 7 showing the pulsing circuit and code selecting equipment and Figure 8 showing the code sounding equipment.

Figures 9 and 10 show the multi-group conference equipment, with Figure 9 showing the group conference finder and Figure 10 shows the group selecting equipment.

Figures 11, 12, 13, 14 and 15 are figure-number diagrams and show the drawing arrangements for the descriptions of the sections entitled Regular P. A. X Service, Key Conference, Code Call, Two Group Conference and Multi-Group Conference, respectively.

Having briefly described the apparatus involved in each figure, a more detailed description of the various operations will follow:

It is to be remembered that the maximum number of lines served by an exchange of this type is 20 lines, and the number of finder connector links may be limited to not more than four. Four lines have been shown, with two parties each and so arranged as to be rung on the opposite sides of the lines. The equipment at each substation consists of the well-known, dial, receiver, transmitter and ringer, therefore only the ringer connections at each substation have been shown, likewise the illustrated substations call numbers. All regular'call numbers are two-digit numbers and assuming that a full capacity of '20 lines are in use and also assuming each line has two parties the call numbers will be arranged in the following order: the digits 31 to 30 and 41 to 40 will be used for the first ten liens and the digits 51 to S0 and 61 to 60 will be used for the second ten lines. The digits 31 to 30 and 51 to 50 will cause the ringing to be applied to the positive line conductors and the digits 41 to 40 and 61 to 60 will cause ringing to be applied to the negative line conductors.

A rotary switch having 26 positions with 25 bank contacts has been utilized wherever applicable in the exchange. The 26th position is the normal home position for the wipers, while the first and second contacts of the connector rotary switch may be used for either code call or two-group conference service, the third and fourth contacts of the same switch utilized for the first digit of the call number when dialling the first group of ten lines and the 15th contact is used as a stopping point for the first digit of the call number when dialling the second group of ten lines. Thus, it will be seen that the first group of ten lines uses contacts through 14 and the second, or last, group of ten lines uses contacts 16 through 25. The rotary switch of the finders (including the code call finder and conference call finder and group selector) are of the non-numerical type and therefore do not use the 26th or home position, whereas, the rotary switch of the connector and code ringing selector are numerical and do use their home positions.

Referring to Figure 1 for the present, the combined line and cut-off relays such as 130, 140, 150 and 160 are actually a two-step relay having two separate and distinct operations, the first operation closing only the x marked contacts and the second operation actuating the remaining contacts. The first operation compares with that of a line relay and the second operation comparing with the action of a cut-off relay.

Referring now to Figure 5, the distributor as shown, is of the rotary type, pre-selecting the next free or idle finder-connector link after each normal operation. Therefore during normal operating periods of the exchange, the wipers of the rotary switch will be resting on an idle link. A busy link will apply a ground potential to the Wipers and hence complete a circuit to the rotary switch motor magnet to cause the magnet to step its wipers off the grounded contact. Therefore, it will be seen that the motor magnet causes the switch to hunt for an absence of ground on its wipers.

It will be remembered that in the illustrated exchange, energization of all the rotary switch motor magnets only prepares the switch for stepping and that the actual stepping of the switch takes place upon the deenergization and release of the magnet.

The illustrated finder-connector link (Figures 3 and 4) has been drawn showing alternative connections to the finder and connector for an exchange including Two- Group Conference Service, or Multi-Group Conference Service, or Code Call Service, the type of special service used being dependent on the requirements of each individual exchange.

Referring to Figures 6, 7 and 8 the finder (Figure 6) of the code call equipment functions nearly the same as the line finder in Figure 3 with the exception that it searches for a ground potential by way of its extra con trol (EC) conductor instead of the control (C) conductor. The rotary switches shown in Figure 7 operate under pulsing during dialing of the code call number. As only the first five contacts of the above-named switches are used, and the code call number contains two digits; the number of codes that can be sent is limited to 25. Therefore, the maximum digital value that either digit can attain is 5. From the foregoing it will be understood that the lowest code call number will be 11 and the highest will be 55. The rotary switches in Figure 8 are of the previously mentioned 25 point type. The push button such as 865 may be conveniently located throughout the building or buildings within which the exchange is installed and may be operated for sounding special alarms such as fire, dismissal signals, etc. The alarms or gongs such as 870 and 880 (as many may be used as necessary) are also conveniently located so as to be clearly audible to everyone.

Referring to Figures 9 and 10 showing the multi-group conference equipment, the conference finder (Figure 9) functions the same as the code call finder. The 26 point rotary switch shown in Figure 10 responds to the group number dialled. As the switch is shown, it is wired for five conference groups, however, it may be wired to include ten conference groups, if desired. From the foregoing, it will be understood that the conference group call number is a single digit and may extend from 1 through 0,

iii

4 though the drawing shows it to be limited from 1 through 5.

The figure-number diagrams 11 through 15 show the arrangement of the drawings for regular, or local, calls and for each special service. It will be remembered that regular calls may be made with each special service or combination of special services.

A detailed operational description of regular calls and all special services will follow, references being had with the drawings which show sufficient apparatus as deemed necessary for each explanation.

Regular P. A. X service The operation of the equipment (excluding all special services) as to the initiation and completion of a regular P. A. X call will now be discussed.

Referring in particular to the figure-number diagram of Figure ll and its associated drawings comprising Figures l, 3, 4 and 5, sufiicient apparatus of the system is shown as deemed necessary for the explanation.

Assuming that subscriber B is given a designated call number such as 32 and that subscriber D desires to call subscriber B, the equipment will operate in the following manner:

When subscriber D removes the receiver, a loop is closed across his talking conductors and a circuit is completed to the line and cut-off relay 169, this circuit extending from ground at contacts 163, the associated positive talking conductor, the loop circuit, the associated negative talking conductor, contacts 161, upper winding of relay and the lower winding of relay 160 to battery. As previously described, the relay 160 is a two-step line and cut-off relay having two serially connected windings, capable (during the present energization) of causing the relay 169 to close only the x contacts. At x contacts 16.2, relay 160 applies battery potential to the control conductor 156. At x contacts 165, relay 160 applies a ground potential to the distributor-start conductor 190, completing a circuit to the distributor-start relay 51!? (providing that the wipers of the distributor motor magnet 575 are resting on an idle finder-connector link), this circuit extending from ground at contacts 164, x contacts 165, conductor 1%, contacts 552-2, high resistance winding of distributor-start relay 510, contacts 501, 5'76 and through the marginal winding of motor magnet 575 to battery. Magnet 575 will not operate in series with relay 510.

As previously mentioned, the distributor is of the rotary type and after each normal operation preselects the next idle or free finder-connector link, therefore wipers S05 and 506 of the associated motor magnet 575 will rest on an idle or free link. However, if all links were busy at the moment, the operating circuit of the all-links-busy relay 5% would be open due to the absence of ground potential (supplied by any idle or free link from ground at contacts such as 354 in Figure 3) on the conductor 557 to relay 500. Relay Still would tic-n restore and open the circuit to motor magnet 575 at contacts Sill, thereby preventing motor magnet 575 from operating. However, as soon as a link becomes free, the ground potential is restored to the conductor 557 and relay 500 will operate and prepare a circuit to motor magnet 575. This circuit will be completed if wiper 505 is resting on a contact terminating the guard lead of a busy link, but if the wiper is resting on a contact terminating the guard lead .of an idle link, the circuit will not be completed. As shown in Figure 5, the wipers 595 and 566 of magnet 575 are resting on the contacts of the illustrated finderconnector link (Figures 3 and 4) which is shown as idle.

In operating contacts 511, distributorstart relay 51) opens a point in the energizing circuit of motor magnet 575, at contacts 512 ground is removed from a secondary kick-oil circuit which is under control of the calling subscriber and relay 53%, at contacts 515 a circuit is completed for relay 526 which at the moment is slightly slow to operate due to its short circuited upper winding.

At contacts 514 relay 510 applies a ground to the multiple circuit for maintaining relay 500 operated, at contacts 515 prepares an operating circuit for the relay 550 and at contacts 516 completes an obvious pro-energizing circuit for relay 550. Resistance R2 is high enough to prevent relay 550 from operating, but making relay 550 quick-acting to any splash of current through its upper winding and operative for any such splash.

In operating, relay 520 completes a circuit for the slowto-operate relay 530, from ground at contacts 521 and at contacts 522 prepares a circuit for relay 560.

In operating relay 530 completes a circuit to the finderstart relay 320 (Figure 3) at contacts 531, this circuit extending from ground at contacts 531, wiper 506 and its associated contact, conductor 547 and the winding of relay 320 to battery. At contacts 532 relay 530 prepares a circuit for motor magnet 575, at contact 533 a kickofi circuit is prepared for motor magnet 575, at contacts 534 the circuit of the upper winding of relay 520 is opened, thereby giving relay 520 a normal quick restoring time interval. At contacts 535 relay 530 connects a ground to the multiple circuit of relay 500 and applies ground at contacts 536, thereby preparing circuits for motor magnet 390 and finder cut-through relay 300.

In operating contacts 321, relay 322 completes an obvious circuit for line relay 330 at contacts 322 a circuit is prepared for the finder cut-through relay 300, at contacts 323 a circuit is prepared for the pro-energized relay 550 and at contacts 324 completes a circuit for the finder motor magnet 390, this circuit extending from ground at contacts 536, contacts 541, 552, conductor 517, contacts 325, 307 and through the winding of magnet 390 to battery.

In operating contacts 331, line relay 330 completes an obvious circuit for the slow-to-release hold relay 340. In operating contacts 341, hold relay 340 prepares a circuit for operating the line and cut-01f relay 160 completely, at contacts 342 a pulsing circuit is prepared to the connector motor magnet 490 and at contacts 343 a point in the release circuit of the motor magnet 490 is opened.

During the operation in the preceding paragraph, magnet 390 in operating completes an obvious circuit to the interrupter relay 540 at contacts 391. Relay 540, in operating contacts 541, opens the previously traced operating circuit of magnet 390, allowing magnet 390 to restore. In restoring, magnet 390 advances rotary Wipers 326, 327, 328 and 329 one step, and opens the circuit to relay 540 by way of contacts 391. In restoring, relay 540 again completes the previously traced circuit to magnet 390 by way of contacts 541. Magnet 390 reenergizes and at contacts 391 again completes the circuit to relay 540. Relay 540 energizes and at contacts 541 opens the circuit to magnet 390 allowing it to restore. In restoring, magnet 390 advances wipers 326, 327, 328 and 329 a second step and at contacts 391 again opens the circuit to relay 540 allowing it to restore. This interaction between magnet 390 and relay 540 continues until wiper 328 engages the contact terminating control conductor 156, at which time a circuit is completed for the preenergized relay 550, this circuit extending by way of ground at contacts 515, upper winding of relay 550, conductor 527, contacts 323, Wiper 328 and its engaged contact, conductor 156, cable C-170, conductor 156, x contact 162 and the lower winding of relay 160 to battery.

In operating contacts 552, relay 550 opens the circuit to magnet 390 and at contacts 551 completes a circuit to the finder cut-through relay 300, this circuit extending from ground at contacts 536, contacts 541, 551 conductor 537, contacts 332 and the winding of relay 300 to battery. At contacts 553 an obvious circuit is completed to the total call meter 585 for registering each call and at contacts 554 a locking circuit of relay 570 is opened. It is to be remembered that wipers 326, 327, and 329 are also resting on contacts in their respective banks corre- 6 sponding to the contact upon which wiper 328 is resting.

In operating contacts 301 and 303, finder cut-through relay 300 completes the extension of the talking conductors from the calling line with the finder-connector link, at contacts 302 a circuit is completed for the transmission of dial tone out over the positive talking conductor to the calling station as an indication of readiness by the link to receive dialling. At contacts 304, relay 300 completes the circuit for the complete operation of relay 160, this circuit extending from ground at contacts 341, contacts 304, wiper 328 and its associated contact, conductor 156, cable C-170, conductor 156, x contacts 162 and the lower winding of relay to battery. The closing of contacts 304 also shunts the upper winding of relay 550, but since relay 550 has operated, it will remain so by the holding effect of its lower winding. The ground potential at contacts 341 busies subscriber D to other finders and is also applied to the rotary connector switch by way of conductor 166 to busy subscriber D to incoming calls. At contacts 305, relay 300 completes an obvious holding circuit for itself by way of ground at contacts 341. At contacts 306, relay 300 prepares a future locking circuit for relays 330 and 400, and supplies a working ground for various other relays in the finder-connector link, at contacts 307 the interrupting circuit to motor magnet 390 is opened, at contacts 308 a circuit is completed for energizing motor magnet 575, this circuit extending from ground at contacts 308, conductor 567, contact and engaged with Wiper 505, contacts 532 and the winding of magnet 575 to battery, and at contacts 309 a point in the circuit of all-links-busy relay 500 is opened. In energizing, magnet 575 opens a point in the normal operating circuit of the distributor start relay 510 at contacts 576.

In operating completely (second-step), at contacts 161 and 163, relay 160 opens its previously traced first-step operating circuit, contacts 164 removes ground from the distributor start conductor and relay 510 restores. In restoring contacts 511, relay 510 closes a point in the normal operating circuit of magnet 575, at contacts 513 the circuit to relay 520 is opened allowing it to restore, at contacts 514, a ground is removed from the multiple circuit of relay 500, at contacts 515 ground is removed from the previously opened circuit of relay 550 and at contacts 516 the pro-energizing and hold circuit of relay 550 is opened, allowing relay 550 to restore. In restoring, relay 550 opens the energizing circuit of relay 300 at contacts 551 and at contacts 553 opens the circuit to meter 585. Relay 300, however, remains energized over its previously traced locking circuit.

In restoring, relay 520 opens the circuit to relay 530 at contacts 521. In restoring, relay 530 opens the circuit to relay 320 at contacts 531, at contacts 532 opens the holding circuit for magnet 575, allowing magnet 575 to restore and rotate its wipers one step. At contacts 535 a ground is removed from the multiple circuit to relay 500 and at contacts 536 the operating circuit of magnet 390 is further opened. Magnet 575' will rotate its wipers until wiper 505 encounters a contact (each corresponding to a finder-connector link) which contains no ground potential and stops thereon.

In restoring, relay 320 opens contacts 321 to remove the bridge from relay 330, but relay 330 remains operated from the closed loop of subscriber D. At contacts 322 the energizing circuit of relay 300 is further opened by relay 320, but relay 300 remains operated over a previously traced circuit from ground at contacts 341. At contacts 323 relay 320 further opens the operate circuit of relay 550 and at contacts 324 the energizing circuit of motor magnet 390 is further opened.

As previously mentioned, dial tone has been transmitted back to the calling subscriber which is an indication that the desired number may be dialled and in this case the two-digit number 32 that has been assigned subscriber B will be dialled.

The tens digit 3 is dialled and the line relay 330 (energized at the beginning of dialling) will de-energize and energize upon receipt of each pulse, for a total of three times each. At the beginning of the first pulse and upon de-energizing, relay 336 opens the circuit to relay 340 at contacts 331, but relay 34%) is slow-to-release and therefore holds operated during dialling. At contacts 332 a circuit is completed to relay 470 and motor magnet 490, these circuits extending respectively from ground at contacts 332, contacts 342, conductor 366, contacts 487, 435, to the left over conductor 368, contacts 352, conductor 367 and the winding of relay 476 to battery and from ground at contacts 332, contacts 342, conductor 366, contacts 487, 435, to the right over conductor 368 and through the winding of magnet 49% to battery.

In operating, relay 470 completes an obvious circuit to relay 460 at contacts 471, at contacts 472 ground is removed from wipers 468 and 469 during the pulsing period and at contacts 473, relay 476 completes a circuit for itself effective during pulsing independent of the busy relay contacts 435. Motor magnet 490 energizes and at contacts 491 opens a point in its interrupter circuit. The interrupter springs of the dialling mechanism have closed and the circuit is again completed to line relay 330 which re-energizes thus releasing magnet 496 and ending the first pulse. In operating contacts 462, relay 460 prepares a circuit to the busy relay 436 and at contacts 464 the pulsing circuit is maintained complete.

At the end of the first pulse and in operating, relay 330 closes the circuit to relay 340 at contacts 331 and at contacts 332 opens the pulsing circuit to motor magnet 496 and relay 476. Relay 470 remains operated, however, due to its slow-to-release characteristics.

As previously stated, wipers 465 to 469, inclusive, are resting on the home or 26th position of the rotary switch actuated by motor magnet 49%, therefore, as magnet 4-96 restores, wipers 465 to 469 inclusive are advanced one step, with the lower halves of the Wipers disengaging their respective contacts and the upper halves of the wipers engaging the first contact of each bank. Off-normal springs 475 close as the wipers leave their home positions and complete a circuit to relay 350.

In operating contacts 351, relay 350 removes dial tone from the calling line, at contacts 352 the former energizing circuit for relay 470 is opened, at contacts 353 a ground is maintained on the conductor from the seized finder to a contact of wiper 505, at contacts 354 ground is removed from the conductor to the all-links-busy relay 560 and at contacts 355 a point in the self-interrupter circuit to magnet 490 is prepared.

At the beginning of the second pulse, the circuit to line relay 330 is again opened, which upon de-energizing completes the formerly traced energizing circuit to motor magnet 490 and the holding circuit to relay 470 at contacts 332. However, the circuit path to the latter has been altered with the respect that closed contacts 473 have replaced opened contacts 352. This has no apparent elfect because as previously stated, relay 4'70 remains operated during pulsing of each digit dialled. Magnet 49%) energizes and opens its self-interrupter circuit at contacts 491. This interrupter circuit has no elfect on the operation at the present and will be discussed later. At the end of the second pulse line relay 31% again energizes and opens the circuit to magnet 490 at contacts 332. In restoring, magnet 490 rotates wipers 465 to 469 inclusive, a second step, at which time the wipers are resting on the second contact of the wipers respective banks.

At the beginning of the third pulse, line relay 336 again de-energizes and completes a circuit, by way of contacts 332, to motor magnet 490 which then energizes. At the end of the third pulse relay 330 again energizes and opens the circuit to magnet 490 at contacts 332. In restoring, magnet 490 rotates wipers 465 to 469 inclusive, a third step, at which time the wipers are resting on the third contact of the wipers respective banks. The dialling of the tens digit 3 has now been completed and the circuit to relay 470 has been opened at contacts 332, thus relay 470 will restore before the second digit has been dialed.

In restoring, relay 470 opens the circuit to relay 469 at contacts 471, thereby allowing relay 460 to restore, at contacts 472 ground is restored to wipers 468 and 469 and a circuit is thereby completed to relay 400, this circuit extending from ground at contacts 306, conductor 365, contacts 472, wiper 468 and engaged contact, conductor 348, contact 384 and through the winding of relay 400 to battery. In restoring contacts 461, relay 460 prepares a circuit for the lower winding of relay 480, at contacts 462 the circuit to the busy relay 430 is opened.

In operating contacts 402 and 404, relay 400 has prepared for ringing current to be transmitted over the positive talking conductor, which eventually will serve to cause the ringer of station B to operate. As the ringer for station B is on the opposite side of the line, this ringer will not operate. At contacts 405, relay 400 completes its own obvious locking circuit and at contacts 406 a circuit is completed to motor magnet 490, this circuit extending from ground at contacts 306, conductor 365, contacts 472, wiper 469 and its engaged contact, contacts 406, conductor 378, contacts 387, conductor 376, contacts 488, 491 and the winding of magnet 490 to battery.

In operating, magnet 490 opens its own energizing circuit at contact 491 and thereby restores. In restoring, magnet 490 rotates wipers 465, to 469 inclusive, one step and closes contacts 491, but the circuit to magnet 490 is now open as wiper 469 is resting on an unused (fourth) contact. However, as wiper 46% engages its next (fourth) contact a circuit is completed to relay 380, this circuit extending from ground at contacts 306, conductor 365, contacts 472, Wiper 468 and its engaged contact, conductor 349 and through the winding of relay 380 to battery.

In operating contacts 331. relay 380 prepares a circuit for the cut-through relay 480, at contacts 382 a circuit is prepared for the lower winding of the switch-through relay 480, at contacts 383 a circuit is prepared for Executive cut-in which will be discussed later, at contacts 384 the operating circuit of relay 4% is opened, at contacts 385 a locking circuit is completed for relay 3%, at contacts 386 a circuit is prepared for relay 4'70 and at contacts 387 the line-group interrupter circuit to magnet 490 is opened.

Before continuing with the present description, it is thought that the busy test circuit should be described more in detail. When calling into the first line group, as either the first digits 3 or 4 of the call number are dialled, relay 386 is operated and at contacts 381 completes a busy test circuit to the busy relay 436 from the 4th contact engaged with wiper 467, conductor 33%, contacts 581, conductor 339, contacts 462 and through the Winding of busy relay 430 to battery. Now, when calling into the second line group, as either the second digits 5 or 6 of the call number are dialled, relay 380 is not operated (because contacts 5 and 6 correspond to lines of the first group which may be busy at the time) until magnet 490 has automatically stepped all its associated wipers to their 15th contacts, at which time relay 339 is operated and at contact 331 completes the above traced busy test circuit. It will be noted that when the first digit of the call number to either line group is 3 or 5, relay 4% Will operate to reverse the ring. When the first digit 3 is dialled and after relay 460 operates, magnet 490 steps its wipers to the 4th contacts to operate relay 380. When the first digit 5 is dialled and after relay 4% operates, magnet 499 steps its wipers to the 6th and subsequently to the 15th contacts before relay 380 operates.

The system is now ready for the second or units digit 9 2, of the call number 32, to be dialled. As the digit 2 is dialled, line relay 33-8 (energized at the beginning of dialling) will de-energize and energize upon receipt of each pulse, for a total or" two times each. At the beginning of the first pulse and upon de-energizing, relay 330 opens the circuit to relay 348 at contacts 331, but as relay 348 is slow-to-release, it will hold operated during dialling. At contacts 332 a circuit is completed to relay 470 and motor magnet 498, these circuits extend respectively; from ground at contacts 332, contacts 342, conductor 366, contacts 487, 435, to the left over conductor 36%, contacts 386, conductor 367 and through the winding of relay 4'70 to battery; from ground at contacts 332, contacts 342, conductor 366, contacts 487, 435, to the right over conductor 368 and through the winding of magnet 49% to battery.

In operating contacts 4711, relay 47b completes a circuit to relay 468, at contacts 472 ground potential is removed from wipers 468 and 469, relays 380 and 488 are locked operated to grounded conductor 365; and at contacts 473 relay 4'78 slightly alters its previous operate circuit. In operating, magnet 4% opens a point in its interrupter circuit. At the end of the first pulse and in operating, relay 338 opens the circuits to relay 470 and magnet 498. Relay 478, however, is slow-to-release and does not restore during pulsing. In operating contacts 462, relay 46d prepares a circuit for busy relay 434) and at contacts 464 the pulsing circuit is maintained complete in case busy relay 438 should operate before pulsing is completed.

At the beginning of the second pulse and in releasing, relay 338 completes the circuit to magnet 498. Magnet 4%, in operating, opens its interrupter circuit at contacts 491 which again have no effect at the present. At the end or" the second and final pulse, relay 338 energizes and opens the circuit to magnet 498 and relay 478 at contacts 332. In restoring, magnet 498 rotates Wipers 465 to 468 inclusive, another step. It will be remembered that at the beginning of the last di it to be dialled, wipers 465 through 469 were resting on the fourth contact of each respective wiper-bank and that the second digit 2 caused the wipers to rotate two additional steps, so now it is evident that the wipers are resting on the sixth contact of each respective bank.

In restoring, relay 478 opens the circuit to the slave relay 468 at contacts 471, at contacts 472 ground is restored to wipers 468 and 469 with no affect and at contact 473 the holding circuit of relay 4747 is opened. During the time that wiper 467 first engages its sixth contact and before the relay 4611' has restored, a busy-test of the called line is made. If the called line should be busy, a ground would be impressed on the called lines control conductor by contacts such as 484 of its associated seized connector. This ground would be encountered by wiper 467 at its sixth contact and complete a circuit to the busy relay 430, this circuit extending from wiper 467, conductor 338, contacts 381, conductor 839, contacts 462 and the winding of relay 430 to battery. Relay 43%), in operating, would close contact 431 for transmitting busy tone out over the positive talking conductor to the calling subscriber, a more detailed description of connection to a busy line being described hereinafter. However, for the present operation, it will be assumed that the called line is not busy, therefore no ground will be encountered by Wiper 467, and busy relay 438 will not operate.

In restoring, at contacts 461 relay 4% completes an operative series circuit to the cut-through relay 488 by way of its lower winding and the line and cut-off relay 148 this circuit extending from ground at'contacts 382, conductor 377, down to contacts 455, contacts 432, through the lower winding of relay 488, contacts 486, 461, conductor 339, contacts 381, conductor 338, wiper 457 and its associated contact terminating conductor 186, cable C488, conductor 186, contacts 118 and the lower winding of relay 148 to battery. In operating, relay 148 opens the circuit to its upper winding at contacts 141, at contacts 142 ground is removed from the positive talking conductor, at contacts 143 subscriber B is busied at the finder banks, and at contacts 144, ground is removed from the distributor start conductor to prevent the distributor from starting a finder.

in operating, relay 480 first closes x contacts 485 and completes an operative locking circuit for relay 480 by way of its upper winding, this circuit extending from 1 ground at contacts 382, conductor 377, x contacts 485 and through the winding of relay 480 to battery. At contacts 481, relay 480 prepares a circuit for ring-back tone, at contacts 482 and 483 the talking conductors of the called subscriber are connected with those of the seized connector and a circuit is completed for ringing current, this circuit extending from the grounded ringer of subscriber B, the positive talking conductor, contacts 112, 116, conductor 184, cable C480, conductor 184, sixth bank contact engaged with wiper 466, contacts 483, 424, 482 and down through the lower winding of the ring cut-off relay 420 to interrupted generator. At contacts 484, relay 480 applies a ground to prepare a circuit through the upper winding of relay 420 and also provides an additional busying ground on the control conductor of subscriber B. At contacts 486, relay 480 opens the energizing circuit through its lower winding, at contact 487 the pulsing circuit is opened and at contacts 488 the interrupter circuit to motor magnet 490 is opened.

After a normal interval of ringing over the previously traced circuit at station B, subscriber B answers the call by removing his receiver. The removal of the receiver at station B closes the switch-hook springs (not shown) at the station and completes a direct current circuit through the lower winding of ring cut-off relay 420 for operating the relay. This circuit extends from ground at contacts 484, 421, 482, wiper 465 and its engaged sixth contact, conductor 181, cable 0-180, conductor 181, contacts 113, 111, negative talking con-ductor, switchhook springs at station B, positive talking conductor con tacts 112, 116, conductor 184, cable C-18tl, conductor 184, wiper 466 and its engaged sixth contact, contacts .83, 424, 402 and through the lower winding of relay 424 to battery at interrupter generator.

In operating, relay 420 looks itself operated by closing its x contacts 426, this circuit extending from ground at contacts 484, conductor 338, contacts 381, conductor 33), x contacts 426 and through the upper Winding of relay 420 to battery. At contacts 423, and 424, ringback tone and ringing current are removed from the calling and called line respectively, atcontacts 422 and 425 the back bridge relay 410 is connected across the called line and the talking conductors of the calling and called line are connected so that conversation may proceed. Line relay 338 supplies talking battery for the calling party and back bridge relay 410 supplies talking battery for the called party.

After completion of conversation, both stations B and D replace their receivers. The replacing of the receiver at station D disconects the equipment in the following manner:

The circuit is opened to line relay 330 which restores and opens the circuit to the hold relay 340 to contacts 331. Relay 340, in restoring, releases contacts 341 and opens the locking circuit to relay 300, and at contacts 343 prepares the self interrupted homing circuit of motor magnet 490. The removal of ground at contacts 341 also releases line and cut-oft relay 160. In restoring, relay 300 opens the locking circuits of relays 380 and 400 at contacts 306 and at contacts 308 removes one of the ground connections from guard lead 567. Relay 380, in restoring removes ground from conductors 377 and 339 by way of contacts 381 and 382, thereby opening the circuits to relays 420 and 480. In restoring contacts 484, relay 490 opens the circuit to relay 140, which restores and at contacts 488 completes the homing circuit to magnet 490, this circuit extending from ground at off-normal springs 475, conductor 375, contacts 355, 343, conductor 376, contacts 488, 491 and through the winding of magnet 490 to battery. Magnet 490 energizes and opens its circuit repeatedly until it has stepped wipers 465 to 469 inclusive to the 26th or home position, at which time off-normal springs 475 open and the circuits to magnet 490 and relay 350 are maintained open. Relay 420 has restored and the equipment is again at rest and ready for future calls.

Executive cut-in Station A is shown as being assigned to an executive and is equipped with a non-locking key such as 178, which provides the executive with executive cut-in on busy lines. This special feature will function as described in the following paragraphs.

It will be assumed that the subscriber at station E has received or initiated a call and is in a busy condition. finder-connector identical to the one shown in Figures 3 and 4 will be in use and associated with station E.

Assuming further that this particular executive desires to call station B, his call will be initiated and handled in the same manner as described in the section entitled Regular P. A. X Service, but stopping at the point in the operation where the last digit 2 of the call number 32 has been dialled and before the release of the slave relay such as 406. It will also be assumed that the illustrated finder-connector link in Figures 3 and 4, will be used in handling the call placed by said executive.

Continuing now with the explanation: After the last pulse of the dialled digit 2 has been received and motor magnet 490 has advanced wipers 465 to 469 inclusive, the Wipers are engaged with their respective sixth ce-n tacts. The circuit to relay 479 has been opened at contacts 332 by the line relay 3% and relay 476 restores.

In restoring, relay 470 opens the circuit to slave relay 460, but relay 460 is slow-to-release and does not restore immediately, thereby utilizing this time interval to test 1 for busy. As previously stated, station E is busy and therefore wipers 467 will encounter ground at its sixth contact which then completes a circuit for the busy relay 430, this circuit extending from the grounded control conductor, wiper 467 and engaged contact, conductor 338, contacts 381, conductor 339, contacts 462 and the winding of relay 430 to battery.

In operating contacts 431, relay 430 completes a previously traced busy tone circuit to station A, at contacts 432 an energizing circuit is opened to the lower winding of relay 489 and at contacts 433, relay 430 prepares a locking circuit for itself. In restoring as the armature of contact 462 starts to release, a locking circuit is completed for relay 430 by relay 460, this circuit extending from ground at contacts 382, conductor 377, contact 455,

433, 456, 463 and through the winding of relay 430 to battery.

After hearing busy tone, the executive momentarily depresses his non-locking key 178, thus completing a circuit to the cut-in relay 450, this circuit extending from ground at key 178, conductor 189, cable 0-170, conductor 189, the fifth contact of the rotary finder switch and wiper 329, contacts 383, 361, conductor 337, contacts 443 and the winding of relay 450 to battery.

In operating, relay 50 completes the extension of station A with station B at contacts 451 and 453, at contacts 452, busy tone is removed from the calling line, at contacts 454 and 455, the holding circuit of relay 430 is changed back to the original busy ground on the contact of the called line and at contacts 456 a circuit is completed for relay 440 in series with relay 43%). The circuit for these two relays may be traced as follows: From ground on wiper 467, conductor 338, contacts 381, conductor 339, contacts 454, 433, the Winding of relay 440, contacts 463 and the winding of relay 430 to battery. In operating,

12 relay 440 supplies a holding ground for the relay 450 by way of contacts 442.

The executive has been connected with station B and condensers C4 and C-5 may serve as monitoring or talking condensers. The executive may continue to converse with station E or he may request that both parties hang up their receivers, at which time, the busy relay 430 and relay 440 will restore and the cut-through relay will operate and station B is rung and connected directly with the executive, when B answers the ring, in the usual manner. With a small exchange and a limited number of tinder-connector links available, the first method is not desirable, because two links would be in use for the duration of the conversation. For that reason, the second method is preferred, because only one link is used and the other is released to handle other calls. Therefore when station B and his called party release their finderconncctor link, station B no longer is busy and ground is removed from wiper 467 and relays 430, 440 and 450 restore and at the same time complete a circuit through the lower winding of relay 480 over a path previously traced in the section entitled Regular P. A. X Service. The remaining operation of the equipment and the release of the equipment is the same as described in the abovementioned section.

It will be noted that this special type of service entitles the executive to cut-in over all regular calls.

At the top of Figure 4 are shown two conductors 337 and 415 labeled thusly-To Voice Paging. The voice paging equipment is not shown, however, due to certain requirements of the exchange, voice paging may be desired for some stations. A key (such as 178 shown at station A) may be used to start the voice paging equipment in the following manner: when the key such as 178 is depressed, operations of the equipment shown in Figures l, 3 and 4 will take place as described in the above section up to and including the operation of relay 440, at which time the closing of contacts 441 completes a circuit to the start relay (not shown) of the voice paging equipment. This circuit may be traced as follows: from ground at key 178, conductor 189, cable C17t conductor 139, the 5th contact engaged with wiper 329, contacts 383, 361, conductor 337, contacts 441, conductor 415 and through the winding of the voice paging start relay (not shown) to battery. The start relay then locks operated to conductor 337, by passing contacts 441.

Upon completion of the voice paging, the operated equipment in Figures 1, 3 and 4 restore as described in the above section.

Code call The ensuing description of the equipment will cover the addition of the special service feature Code Call to the system. This feature is illustrated in Figures 6, 7 and 8 and will be used in combination with Figures 1, 3, 4 and 5, including occasional references to the previous section entitled Regular P. A. X Service.

It will be remembered that certain subscribers whom it is desired to page by code ringing of the code call equipment, are assigned individual designated two-digit code call numbers and that any subscriber wishing to initiate a code call must prefix the single digit 1 to the code call number of the desired subscriber. Only certain stations having their extra control (E. C.) conductor marked, by

having it connected to the code call finder, can initiate a code call, whereas a code call may be answered from any station of the system. The prefix digit 1 should be dialled then a slight pause to wait for a second dial tone before dialling the code call number. Also, it is to be remembered that the code call may be answered by dialing the single digit 2.

It will be assumed that the subscriber at station A is an executive and has been assigned the code call number 33. Assuming also that the subscriber at station C wishes to talk with the executive and has dialled the executives regular call number 41, but has been in- 13 formed by his secretary that he is somewhere at large about the building. The subscriber at station C can now initiate a call for the executive by momentarily replacing his receiver, then removing it and dialling the digit 1" and waiting for dial tone, prior to diallng the code call number 33.

The operaton or" the equipment up to and including the dialling of the digit 1 is the same as that in the section entitled Regular P. A. X Service. A short review upon completion of dialling the digit 1 will reveal that wipers 465 through 469 have been advanced to engage their respective first contacts; relay 470 has restored contacts 472 and completed circuits to relays 380 and 360 and also opened the circuit to relay 460, the circuit for relay 360 extends from ground at contacts 306, conductor 365, contacts 472, wiper 469 and engaged first contact, conductor 369 and the winding of relay 360 to battery; relay 460 in restoring contacts 461 completes a circuit for the lower winding of relay 480 to operate in series with parallel connected relays 630 and 640 of Figure 6, this circuit extending from ground at contacts 382, conductor 377, contacts 455, 432, lower winding of relay 480, contacts 486, 461, conductor 339, contacts 381, conductor 338, wiper 467 and engaged first contact, conductor 781, cable -690, conductor 781, contacts 731, 752, conductor 608, contacts 651 and the windings of relays 630 and 640 to battery. In operating contacts 361, executive cut-in privileges are removed by relay 360, and at contacts 362 prepares an operating circuit for relay 370 and the code call finder. In operating, relay 480 completes its own locking circuit by way of its upper winding and x contacts 485 over an obvious path, at contacts 484 a maintaining ground is applied for the relays 630 and 640, and at contacts 487 opens the pulsing circuit to motor magnet 490.

In operating, relay 640 operates at the same time or ahead of relay 630, thereby preventing relay 650 from operating at thepresent time by opening contacts 641. At contacts 631, relay 630 completes a circuit for relay 610, this circuit extending from ground at contacts 631, contacts 621, 666 and the winding of relay 610 to battery. Contracts 631 also close a pre-energizing circuit for the upper winding of relay 620 through resistor R-3 which renders relay 620 extremely fast to operate. At contacts 632 a battery potential is applied for marking the extra control conductor to prepare for stopping the code call finder on the calling line, and at contacts 633 a circuit is prepared for the relay 650.

In operating, relay 610 completes an obvious circuit for the motor magnet 665 at contacts 611. Magnet 665, in operating, opens the circuit to relay 610 by way of contacts 666. In restoring, relay 610 opens the circuit to magnet 665 at contacts 611. In restoring, magnet 665 completes the circuit to relay 610 by way of contacts 666 and rotates wipers 613 through 616 one step. Relay 610 again completes the circuit to magnet 665 at contacts 611 and magnet 665 then opens the circuit to relay 610 at contacts 666. In restoring contacts 611, relay 610 opens the circuit to magnet 665 and in restoring, magnet 665 again completes the circuit to relay 610 at contacts 666 and again rotates wipers 613 through 616 one more step. This inter-action continues until the last release of magnet 665 rotates wiper 616 to engage the contact terminating conductor 364, at which time a circuit is completed for the pro-energized relay 620 in series with relay 370, this circuit extending from ground at relay 370 and through its winding, conductor 346, contacts 434, conductor 345, contacts 362, 383, wiper 329 and engaged contact, conductor 364, cable C-311, conductor 364, the contact engaged by wiper 616, lower winding of relay 620 and contacts 632 to battery. Relay 620 operates before relay 610 has had time to reoperate and opens the circuit to relay 610 at contacts 621, at contacts 622 the resistance R-3 is shunted to complete an obvious locking circuit for relay 620 by way of its upper winding and at contacts 623 a ground is applied to the control conductors of station C to maintain the line and cut-ofi' relay operated and to busy station C to all incoming calls.

In operating contacts 371, relay 370 initiates the release of the illustrated finder-connector link (which has been seized by station C) by releasing relay 300, which now disconnects the talking conductors of station C from the line relay 330 of the regular finder-link at contacts 301 and 303 and at contacts 366 ground is removed from conductor 365 allowing relay 330 to restore. Line relay 330 restores and opens the circuit to slow-to-release relay 340. Relay 330 opens the locking circuit of relay 480 at contacts 382 and at contacts 383 opens the circuit to the lower winding of relay 620 which now remains operated over its upper winding, the same contacts (383) open the circuit to relay 370. In restoring contacts 484, relay 480 removes the holding ground from relays 630 and 640 and at contacts 488 the self-interrupting circuit for motor magnet 490 is prepared. Relay 340 now has restored and at contacts 343 completes the self-interrupting circuit for motor magnet 490. Magnet 490 restores wipers 465 through 469 to their home position in the manner as described in the section entitled Regular P. A. X Service, and off-normal springs 475 are opened, thereby breaking the circuit to relay 350. The finderconnector link is now completely restored and conditioned to handle future calls.

Referring now to the code call equipment, relay 640 restores ahead of the slow-to-release relay 630, thereby completing an obvious circuit to relay 650 by way of contacts 641. In operating, at contacts 651, relay 650 further opens the circuit to relays 630 and 640, at contacts 652 ground is applied to the control conductor 781 for busying the code call equipment, at contacts 653 a point in an alarm circuit is opened, at contacts 654 and 655 the talking conductors of the calling station C are bridged across and operate line relay 660 and at contacts 656 dial tone is projected out over the negative talking conductor in an obvious and wellknown manner to indicate to the subscriber at station C that the code call number 33 of station A may be dialled. However, before dialling takes place, relay 660 completes an obvious circuit to the hold relay 700 by way of contacts 661. Relay 700, which remains operated during dialling, completes an obvious circuit to the relay 710 by way of contacts 701 and at contacts 702 prepares a point in the pulsing circuit. In operating, at contacts 711 relay 710 opens a point in the right hand winding of relay 750, at contacts 712 a point in the energizing and locking circuits of relays 720 and 730 is prepared, at contacts 713 a locking circuit for the relay 650 is completed before relay 630 is fully restored, at contacts 714 a circuit is prepared for relay 745, at contacts 715 a ground is applied to the control conductor to serve as the previously mentioned ground applied by the relay 620 at contacts 623, and at contacts 716 a point in the left hand Winding of relay 750 is opened. Relay 630 now restores and at contacts 631 opens the circuit to relay 620, at contacts 632 the battery potential is removed from the extra control (E. C.) conductor and at contacts 633 the original energizing circuit to the relay 650 is removed. In releasing, relay 620 removes the ground from the control conductor at contacts 623, however, this conductor remains grounded at contacts 715.

The first digit 3. of the code call number 33 is now dialled and line relay 660 responds to the three dial pulses in a Well-known manner. At the beginning of the first pulse, relay 660 restores and at contacts 662 completes circuits to relay 745 and motor magnet 760, these circuits extending respectively from ground at contacts 662, conductor 648, contacts 702, conductor 668, contacts 604, conductor 678 and (1) 15 down through contacts 714, 738 and through the winding of relay 745 to battery, (2) to the right through contacts 726 and up through the winding of motor magnet 760 to battery. Relay 745 is slightly slow-torelease and therefore remains operated only during pulsing. At contacts 746 relay 745 opens the energizing circuit to relay 720 during pulsing. Motor magnet 760 energizes and prepares to rotate its wipers 785, 786 and 787 one step upon de-energizing. At the end of the first pulse, relay 660 re-energizes and opens the circuits to relay 745 and motor magnet 760 at contacts 662. Relay 745, however, remains operated and in releasing, motor magnet 768 rotates its Wipers 785, 786, and 787 one step.

At the beginning of the second pulse, relay 660 again releases and completes the previously mentioned circuit to relay 745 and magnet 768 via contacts 662, whereby magnet 760 energizes and prepares to rotate its wipers a second step. At the end of the second pulse, relay 660 re-energizes and opens the circuits to relay 745 and magnet 760 at contacts 662. Magnet 760 de-energizes and rotates its Wiper a second step.

At the beginning of the third and last pulse of the first digit, relay 660 again releases and completes the previously mentioned circuits to relay 745 and magnet 760 via contacts 662, whereby magnet 76!) energizes and prepares to rotate its wipers a third step. At the end of the third pulse, relay 668 re-energizes and opens the circuits to relay 745 and magnet 76%) at contacts 662. Magnet 760 tie-energizes and rotates its wipers a third step. Relay 745 in releasing after an interval completes an energizing circuit to the relay 720, this circuit extending from ground at contacts 601, conductor 628, contacts 712, 746, wiper 785 and engaged third contact, contacts 724 and the winding of relay 728 to battery. In operating at contacts 721, relay 720 opens the self-interrupting circuit of magnet 760, at contacts 722 an alarm circuit for the lamp 790 is prepared, at contacts 723, a locking circuit is completed and contacts 724 are opened to break the previous energizing circuit, at contacts 725 a pulsing circuit to the motor magnet 765 is prepared, at contacts 726 the pulsing circuit to motor magnet 768 is opened and at contacts 727, dial tone is removed from the calling line.

The second digit 3 of the code call number 33 is now dialled and line relay 660 responds to the three dial pulses as previously described. At the beginning of the first pulse, relay 66d releases and at contacts 662 completes circuits to relay 745 and motor magnet 765, these circuits extending respectively from ground at contacts 662, conductor 648 v contacts 702, conductor 668, contacts 604, conductor 678 and (1) down through contacts 714, 738 and through the Winding of relay 745 to battery, (2) to the right through contacts 725, 737 and down through the winding of relay 765 to battery. Relay 745 is slightly slow-to-release and therefore remains operated only during pulsing. At contacts 746 relay 745 opens the energizing circuit to relay 738 during pulsing. Motor magnet 765 prepares to rotate its wipers 795, 796 and 797 one step upon deenergizing. At the end of the first pulse, relay 660 reenergizes and opens the circuit to relay 74-5 and motor magnet 765 at contacts 662. Relay 745, however, remains operated and in releasing motor magnet 765 rotates its wipers 795, 796 and 797 one step.

At the beginning of the second pulse, relay 660 again releases and completes the previously mentioned circuits to relay 745 and magnet 768 via contacts 662, whereby magnet 765 energizes and prepares to rotate its wipers a second step. pulse, relay 660 re-energizes and opens the circuit to relay 745 and magnet 765 at contacts 662. Magnet 765 rile-energizes and rotates its wipers a second step.

At the beginning of the third and last pulse of the second digit, relay 668 again releases and completes the pre- At the end of the second viously mentioned circuits to relay 745 and magnet 765 via contacts 662, whereby magnet 765 energizes and prepares to rotate its wipers a third step. At the end of the third pulse, relay 666 re-energizes and opens the circuits to relay 745 and magnet 765 at contacts 662. Magnet 765 de-energizes and rotates its wipers a third step. Relay 745 in releasing completes an energizing circuit to the relay 738, this circuit extending from ground at contacts 681, conductor 628, contacts 712, 746, wiper 797 and engaged third contact, contacts 735 and the winding of relay 730 to battery. In operating contacts 732, relay 730 applies a ground to conductor 781 for busying the code call equipment to other initiated code calls, at contacts 733, an alarm circuit for the lamp 798 is prepared, at contacts 734 a locking circuit is completed and contacts 735 are opened to break the previous energizing circuit, at contacts 736 a marking ground is applied to Wipers 787 and 795 and out over their respective conductors 773 and 778, at contacts 737 the pulsing circuit to magnet 765 is opened, at contacts 738 the energizing circuit to relay 745 is opened, at contacts 739 a circuit is completed for relay 820 and at contacts 740 a point in the self-interrupter circuit to magnet 765 is opened. The circuit to relay 820 extends from ground at contacts 852, conductor 744, contacts 739, conductor 743, contacts 857, 803 and the winding of relay 820 to battery.

In operating contacts 821, relay 820 completes a circuit to the motor magnet 855, this circuit extending from ground at contacts 852, conductor 744, contacts 739, conductor 743, contacts 821 and through the winding of magnet 855 to battery. In operating contacts 857, magnet 855 opens the circuit to relay 828. Relay 820, upon restoring, opens the circuit to magnet 855 at contacts 821. Magnet 8S5 upon restoring, rotates its wipers 885, 886 and 887 one step and completes the circuit to relay 820 via contacts 857. In reoperating, relay S20 completes the previously traced circuit to magnet 855 at contacts 821. In operating, magnet 855 opens the circuit to relay 820 at contacts 857 and relay 820 in releasing contacts 821 opens the circuit to magnet 855. In restoring, magnet 855 rotates its wipers 885, 886 and 887 a second step and recompletes the circuit to relay 820 via contacts 857. In operating, relay 820 completes the circuit to magnet 855 by way of contacts 821 and in operating, magnet 855 opens the circuit to relay 820 by way of contacts 857. In releasing, relay 820 opens the circuit to magnet 855 by way of contacts 821 and in releasing, magnet 855 rotates its wipers 885, 886 and 837 a third step and completes the circuit to relay 820 at contacts 857. In operating, relay 820 completes the circuit to magnet 855 by way of contacts 821 and in operating, magnet 855 opens the circuit to relay 820 by way of contacts 857. In releasing, relay 826 opens the circuit to magnet 855 by Way of contacts 821. In releasing magnet 855 rotates its aforementioned wipers a fourth additional step and at wiper 886 a circuit is completed for the relay 8%, this circuit extending from ground at contacts 736, wiper 787 and its engaged third contact, conductor 773, fourth contact and E engaged wiper 886 and through the winding of relay 8% to battery. Magnet 855 also completes a circuit to relay 829 by way of contacts 857, but as relay 828 is relatively slow-to-operate, relay 800 will operate and open the circuit to relay 820 at contacts 803. At contacts 801, relay 800 locks up to the ground at contacts 852 over the previously traced circuit, at contacts 802 a circuit is completed from ground at contacts 852 over the previously traced circuit to energize relay 810 and at contacts 804 a circuit is prepared for the relay 860. At contacts 811 relay 810 completes a circuit for relay 820 from the locking ground of relay 800 over an obvious circuit, at contacts 812 a splash of dial tone is sent out over the calling line, thereby permitting the caller to know that the code machine is sending out the code.

In operating, relay 820 completes a circuit to the motor magnet 855 by way of contacts 821. In operating, motor 

